fix MSVC /Wp64 warning about size_t to int conversion (closes #10068)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@56621 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/richtext/richtextbuffer.h

@@ -705,7 +705,7 @@ public:
     virtual int GetParagraphLength(long paragraphNumber) const;
 
     /// Get the number of paragraphs
-    virtual int GetParagraphCount() const { return GetChildCount(); }
+    virtual int GetParagraphCount() const { return static_cast<int>(GetChildCount()); }
 
     /// Get the number of visible lines
     virtual int GetLineCount() const;